By standard I meant an error type that implements std::error::Error.

EDIT: Which I assume all my dependencies have done, given that anyhow is able to consume all of them.

I specifically called out writing applications as my use case: my only objection to tptacek's note is the somewhat universal "in practice". The burden for designing errors for a library that others will use is higher, but that's far from the default/universal experience.

Many more people are going to consume libraries & not produce any of their own, and I think my experience is representative there.